High performance sports racquets have a hollow tubular wall made of graphite material. To make such racquets, an elongated tube of pre-preg, formed of uncured graphite, is placed in a mold in the desired shape of the racquet frame. A bladder placed inside the pre-preg tube is inflated, such that the pre-preg assumes the shape of the mold, and the mold is heated to cure the epoxy resin and harden the frame.
After the frame is made, holes are drilled through the opposing walls of the tubular frame to support the ends of the racquet strings. If left uncovered, the sharp edges of the string holes would cause serious string breakage problems. For such reason, composite sports racquets employ plastic grommet strips to prevent direct contact between the strings and the holes in the frame. The grommet strips ride in a stringing groove formed along the outside surface of the racquet head portion, and contain a plurality of hollow grommet pegs, which extend through the holes in the frame. When the racquet is thereafter strung, the strings exit through the hollow barrels of the grommet pegs, and bear against the grommet strip along the outside of the racquet until reaching the next string hole, in this manner avoiding direct contact with the graphite frame.
Prior to Howard Head U.S. Pat. No. 3,999,756, tennis racquets had a relatively small head. When the original grommets were conceived, problems of excess weight did not exist because heavier frame weights were acceptable with smaller head sizes. The '756 patent discloses increasing the relative length and width of the head without increasing the overall racquet size, and today virtually all adult tennis racquets are made utilizing such racquet geometry. However, with the increased head size, the additional weight of the grommet strips and bumper strips became a recognized problem.
Over the years, newer, stiffer frame materials, together with advances in molding techniques, have allowed composite sports racquets to become increasingly light. Today's graphite tubular frames as molded are very strong and very stiff, even with very thin wall thicknesses. However, when racquet string holes are subsequently drilled in the racquet, carbon fibers are broken and the frame is weakened locally. This problem is exacerbated by the fact that the string holes must have a diameter large enough not just for a string, but for a plastic grommet peg. As frame walls have become increasingly thin, the process of drilling the string holes can weaken the frame significantly, to the point where the frame is unable to support the high forces of the tensioned strings, resulting in strings pulling through the walls of the frame tube.
Frame tubes also can fail after impact with a hard surface, such as the court surface, because such impact can produce cracks. For such reason, it is customary to provide grommet strips, in the outer region of the frame, with a pair of flanges covering the frame surface (such grommet strips being known as "bumper strips"), to help protect the frame from such impacts. These flanges add additional weight at the tip region, which is undesirable. Moreover, as tube walls have become thinner, they are more prone to impact damage, even with a bumper strip present.